The invention relates to a magnetic-tape cassette for a magnetic-tape apparatus, which cassette comprises at least one electrically conductive cylindrical tape guide which is arranged to be movable to a limited extent and which is formed with at least one axial recess which is accessible from the exterior of the magnetic-tape cassette. The magnetic tape passes with its base side along a part of the circumferential surface of the tape guide with its base side contacting that surface. An electrically conductive locating pin is arranged on the apparatus and is at the reference potential of the apparatus. The locating pin engages the recess in the tape guide upon insertion of the magnetic-tape cassette into the magnetic-tape apparatus. Such a magnetic-tape cassette is for example described in U.S. Pat. No. 4,234,140 (herewith incorporated by reference), which also describes how the magnetic-tape cassette can be inserted into the magnetic-tape apparatus: that is, how it can be brought into its operating position, so that the locating pin on the apparatus engages the recesss in the tape guide and accurately defines the position of the cassette, which as is known is essential for a correct tape transport.
A problem with such magnetic-tape cassettes is that the coating side of the magnetic tape may be charged electrostatically, which gives rise to problems during operation. In order to drain such electrostatic charges it has been proposed in German Offenlegungsschrift No. 30 10 772 to provide a grounding element inside the cassette. The element is in contact with the coating side of the magnetic tape and, when the magnetic-tape cassette is inserted into the magnetic-tape apparatus from outside the magnetic-tape cassette, comes into electrically conductive contact with an electrically conductive part of the apparatus which is at reference potential. For this purpose U.S. Pat. No. 4,285,020 (herewith incorporated by reference) describes some constructions, one of these constructions being to arrange an electrically conductive strip-shaped resilient element in the magnetic tape cassette. One end of the element pressed against the coating side of the magnetic tape which extends between two tape guides, and the other end projects through an opening in the side wall of the magnetic tape cassette. Upon insertion of the magnetic-tape cassette into the magnetic-tape apparatus, this other end can come into electrically conductive contact with a leaf spring on the apparatus. Another construction comprises a pivotable lever arranged in the magnetic-tape cassette, a pin-shaped end of this lever being in contact with the coating side of the magnetic tape which extends between two tape guides and the other end, upon insertion of the magnetic-tape cassette into the magnetic-tape apparatus, coming into electrically conductive contact with a locating pin which then penetrates into the magnetic-tape cassette. This locating pin positions the entire magnetic-tape cassette.
It is evident that the steps for draining an electrostatic charge from the coating side of the magnetic tape proposed in DE-OS No. 30 10 772 are comparatively intricate and expensive. This is particularly disadvantageous because such magnetic tape cassettes are mass products, and should be as cheap as possible.